consolidate hpt(), host2ip(), and their use

[janstary]

• put them both into utils.c
• reflect that in the win/*proj files
• require the RTP port to be even
• pass sockaddr_in to hpt()
• use hpt() in rtptrans instead of duplicating it
• make host2ip() return int as an indication, not an address of -1
• various cleanups

Tested on OpenBSD, Debian, Gentoo and Solaris

[mcd500]

I have not built and checked them but great improvements. It looks fine by seeing the code. Thanks, merging.